The present invention relates to a bump forming apparatus for forming bumps on semiconductor wafers, and a bump formation method carried out by the bump forming apparatus.
In recent years, electronic components have been made more and more compact in accordance with miniaturization of devices, e.g., portable phones and the like on which the electronic components are mounted. Thus, there is a bump forming apparatus for this purpose which forms bumps to electrode portions at each circuit formation part on a semiconductor wafer without separating the circuit formation part from the semiconductor wafer. The bump forming apparatus of this kind includes a carry-in device for taking out a semiconductor wafer before bumps are formed thereto from a first storage container where the semiconductor wafers without bumps are stored, a second storage container for storing wafers with the bumps formed, a bonding stage where wafers without bumps are placed and heated generally to about 250-270xc2x0 C. so as to join the electrode portions and bumps, a carry-out device for storing the wafers after the bumps are formed thereon into the second storage container, and a transfer device for transferring the wafers from the carry-in device to the bonding stage and from the bonding stage to the carry-out device.
Meanwhile, as a SAW (Surface Acoustic Wave) filter used in the aforementioned portable phones and the like, there are some semiconductor wafers having a substrate of the wafer not formed of silicon as in the prior art but formed of quartz, or a compound semiconductor wafer such as lithium tantalum, lithium niobium, gallium arsenide or the like. Although the compound semiconductor wafer of this type is heated as well to approximately 150xc2x0 C. at maximum in forming the bumps, it is necessary for the heating and cooling speed of the compound semiconductor wafer to be lowered in comparison with the conventional silicon wafer. Unless the cooling is carried out slowly, the compound semiconductor wafer is accompanied by a pyroelectric effect thereby breaking circuits, or the wafer is thermally deformed to crack in some cases.
As such, a bump forming apparatus for forming bumps to the compound semiconductor wafers needs a different way of temperature control from the control in the conventional bump forming apparatus which forms bumps to silicon wafers.
The present invention has for its object to provide a bump forming apparatus which executes temperature control different from the prior art before and after forming bumps to semiconductor wafers, and a bump formation method carried out by the bump forming apparatus.
In order to accomplish the above and other objects, a bump formation method is provided according to a first aspect of the present invention for forming bumps onto electrodes of a circuit formed to a semiconductor wafer. In the bump formation after bonding the bumps on the semiconductor wafer by practical heating for bump formation and method, before storing the semiconductor wafer in a storage container, a post-heating operation in which a temperature drop of the semiconductor wafer is controlled is performed on the semiconductor wafer.
In a second aspect of the present invention, a preheating operation is performed on the semiconductor wafer before the semiconductor wafer is practically heated in addition to the bump formation method of the first aspect.
In a bump formation method according to a fifth aspect of the present invention, before the bump bonding is carried out after the semiconductor wafer is placed on a bonding stage which heats the semiconductor wafer to a temperature for bump bonding in the practical heating, a temperature difference between a temperature at a side of a stage contact face of the semiconductor wafer in contact with the bonding stage and a temperature at a side of a circuit formation face of the semiconductor wafer opposite to the stage contact face may be controlled in addition to the bump formation method of the first aspect. Thus, the semiconductor wafer placed on the bonding stage is maintained within a warpage non-generation temperature range in which a warpage of the semiconductor wafer is restricted to a level not obstructing the bump formation.
A bump forming apparatus provided according to a third aspect of the present invention has a bonding stage where a semiconductor wafer is placed and which practically heats the semiconductor wafer to a temperature for bump bonding necessary to form bumps on electrodes formed to a circuit of the semiconductor wafer. In addition, a bump forming head is placed above the bonding stage for forming the bumps onto the electrodes of the semiconductor wafer, and a load and transfer device is provided for putting and removing the semiconductor wafer on the bonding stage. Furthermore, a post-heating device is provided for cooling the semiconductor wafer based on a temperature drop control to the semiconductor wafer after bumps are bonded on the practically heated semiconductor wafer.
In a bump forming apparatus according to a fourth aspect of the present invention, a preheating device can be additionally provided for the bump forming apparatus of the third aspect for carrying out a preheating operation on the semiconductor wafer before the semiconductor wafer placed on the bonding stage is heated to the temperature for bump bonding.
A bump forming apparatus according to a sixth aspect of the present invention may have a wafer temperature control device added to the bump forming apparatus of the third aspect. Before the bump bonding is carried out after the semiconductor wafer is placed on the bonding stage, the wafer temperature control device controls the temperature difference between a temperature at a side of a stage contact face of the semiconductor wafer placed on the bonding stage in contact with the bonding stage and a temperature at a side of a circuit formation face of the semiconductor wafer opposite to the stage contact face so that the temperature difference is within a warpage non-generation temperature difference range where a warpage of the semiconductor wafer is restricted to a level not obstructing the bump formation.
According to the bump formation method in the first aspect and the bump forming apparatus in the third aspect of the present invention,the post-heating device executes the post-heating operation for controlling a temperature drop of the wafer after bumps are formed on the wafer. Thus, generation of troubles such as a circuit break due to a pyroelectric effect, a crack by thermal deformation and the like can be prevented even when compound semiconductor wafers sensitive to a temperature change are handled.
In the bump formation method of the second aspect and the bump forming apparatus of the fourth aspect of the present invention, the preheating device is further provided in addition to the post-heating device, thereby heating the semiconductor wafer while controlling a temperature rise of the wafer before bumps are formed on the wafer. Thus, even when compound semiconductor wafers sensitive to a temperature change are handled, generation of troubles such as a circuit break by a pyroelectric effect, a crack by thermal deformation and the like can be further prevented.
In the bump formation method of the fifth aspect and the bump forming apparatus of the sixth aspect of the present invention, the wafer temperature control device is additionally set to execute temperature control on the semiconductor wafer placed on the bonding stage to suppress a warpage of the semiconductor wafer to a level not obstructing the bump formation. Thus, the semiconductor wafer can be maintained in a nearly flat state even at high temperatures, e.g., 200-250xc2x0 C., so that bumps can be formed on the semiconductor wafer at the high temperatures.